Modified cross section yarn



Nov. 9, 1965 J. E. OPFELL 3,216186 United States Patent O 3,216186 MODIFIED CROSS SECTION YARN James E. Opfell, Colonial Heights, Va., assignor t Allied Chemical Corporation, New York, N.Y., a corporation of New York Filed May 14, 1963, Sex. N0. 280,321 2 Claims. (Cl. 57140) This invention relates to nove1 multifilament thermoplastic yarns having improved visual appearance, and particularly to lustrous yarns of adjustable bulk consisting of a multitude cf crimped continuous filaments of novel cross sectional configuration, and to the production therefrom of tufted carpets.

In the production of high quality textile floor coverings such as rugs, carpets, and the 1ike, it is generally sought to achieve good resiliency, high covering power, and resistance to soiling. Another quality frequently sought is a visual luster highlight 0r sparkling elfect in the carpet surface. Securement of resiliency and c0vering power with continuous filarnent yarn has generally been sought by utilization of yarns having individual filarnents of greater than about 7 -denier, and wherein the texture or bulk of the yarn has been increased by crimping prior t0 incorporation into carpet -structures. lt is found however that yarns having the requisite bulk to produce good carpet characteristics d0 not process well in manufacturing operations such as tufting wherein the yarn must pass through narrow eyes of needles in the course of carpet manufacture.

It has been recognized that latent bulking characteristics may be imparted to carpet yarns by chemical or physical modifieation which develops mechanical crimping forces during carpet dyeing at elevated temperatures, to improve covering power and resiliency. Yarns having such latent propensity to become bulkier upon exposure to relaxing conditions of elevated temperature and 110 tensile restraint generally undergo a shrinkage with consequent increase in relaxed yarn denier. It has been found however, that although a certain amount of bulking produces desirable improvements in yarn covering power and carpet resiliency, an excessive amount of yarn shrinkage leads to undesirable lass of pile height, resulting in a matted carpet appearance frequently referred to as pull down.

Various filament cross sectional configurations have been employed to secure certain physical and aesthetic property improvements in carpets. For example, centrally symmetrical filaments having triangular or multilobal cross sectional configurations have been studied in efforts to secure improved carpet resiliency in view of the higher bending modulus or stiffness of said modified lilaments. Cross sectional configurations containing straight portions in a multi-vaned, multi-lobed, or polygonal pattern have been studied in efforts to secure enhanced optical qualities such as reflectivity or luster highlight. Typical configurations containing straight portions are disclosed in U.S. Patents 2637,893; 2828752; 2939201; and 2,317,485. It has been found however that previous departures frorn the conventional round cross section are not without adverse eifects on processability, latent yarn bulking properties, or the response of the latent properties to finishing operations.

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It is an object of this invention to provide a n-ovel yarn having improved viual appearance.

It is anofher object of this invention t0 provide a textured continuous thermoplastlc yarn having -pronounced luster highlights and acceptable processability in carpet tufting operations and which after incorporation into a textile structure, can be treated at elevated temperature so as to develop improved resiliency and covering power.

It is 21 further object of this invention to provide a process for the production of bulked polycaproamide yarns -of novel cros-s sectional configuration useful in the production of tufted carpets which can be thermally treated to develop improved resiliency and covering power. Other objects and advantages will becorne apparent hereinafter.

It has now been found that filament cross sectional configurations which possess th1ee lobes having a line 0f symmetry instead of a center of symmetry, and having the particular geometry below defined afford filaments of high bending modulus which, when provided with periodic sites of inter-crystalline strain and disorientation, exhibit a controlled increase in bulk in response to yarn relaxing conditions. By utilizing the eflect of the special cross sectional configuration, in combination With other filament and polymer characteristics, I have found, a yarn is provided which not only processes well in tufting operations, but rnoreover produces carpet structures of good covering power, resiliency and improved luster highlight.

The invention will be better understood by reference to the drawings which illustrate preferred embodiments of the invention, and wherein:

FIG. 1 is a magnified sectional view of a trilobal filament in accordance With this invention. As shown in FIG. 1, the peri-phery cf the cross section can be regarded as being formed from three circles centered at A, B, and C. In the figure, these circles are cornpleted by dotted lines; and points =of inflection on the periphery passing from one to the next circle are indicated at A and A"; B and B"; C and C".

FIG. 2 is a magnified section of a multifilarnent yarn of this invention, -showing how the filaments pack together -by reason of the particular cross section.

FIG. 3 is a plan view of a spinneret 1 suitable for producing the multifilament yarn of the invention.

FIG. 4 shows in sectional elevation a typical orifice of the spinneret, consisting of cylindrical inlet pa-ssage 2 leading to a group of three holes 3, forming an isosceles triangle.

FIG. 5 i-s an enlarged lan view showing the arrangement of the holes 3 at the base of inlet passage 2, the apex hole of the isosceles triangle being at the center of assage 2. The centers of these holes are indicated at A, B, C to -correspond With the centers of the lobes produced from the respective holes as indicated in FIG. 1.

Referring to FIGURE 1, the points A, B, and C represent the Centers of curvature 0f the three individual lobes, the lobes centered at A and C having substantially the same radius of curvature (r); and that centered at B having radius of curvature from /2 to 2 fold r, and preferably about equal to r. The points A", B", and C", etc. define inflection points 0n the circular arc of each lobe. An inverse curvature is found between inflection points A'B' A and C", and B" and C.

For oonvenience of definition the lobe defined by center of curvature B may be referred to as the center lobe, and the other lobes Will be referred to as pendant lobes. The lines of centers drawn between B and A, and between B and C are essentially equal in length and define the extension f the centers of the pendant lobes from the center of the, center lobe. This distance, for oonvenience of discussion, will hereinafter be referred to merely as the extension. The intersecti-on of the extension lines defines the included angle alpha (u). The bisector line 0f angle (a) bis-f:cts the most pronounced of the three sectors of inverse eurvature, A"C" and constitutes the axis of symmetry for the everall configuration.

In accordance With this invention, a trilobal cross-section of a yarn filament as in FIGURE 1 is provided, having the three lobes separated by peripheral arcs of inverse curvature which arcs between the center lobe and pendant lobes are essentially identical and have larger radii of inverse curvature than does the arc between two pendant lobes; and wherein the angle (es) is between 80 and 120; the lobe radius, r, is generally, and especially for carpet yarn, in the range from about 5 to about 20 microns; the ratio of lobe radius to extension is between 0.60 and about 1; and the total circular arc A'A", B'B, C'C is between 400 and 800.

Among the filaments of a yarn, the cross sections Will vary more or less. I prefer that substantially all filaments of a Single yarn of my invention have cross sections Within the above ranges; and on the average have circular arc of about 400600 and included angle (a), of about 90, and ratio of lobe radius; extension of about 0.81.0 corresponding to the two pendant lobes being formed from overlapping circles and the center lobe being formed from a circle cutting about midway through the overlapping area of the other two circles, the three circles having substantially equal radii.

The measurements and geometry of cross sections of filaments in accordance with this invention can be obtained by measuring plmotomicrographs of sections of the filaments, at known magnification. The values referred to herein, unless otherwise specified, are to be understood as being average values, averaged over about 20 filaments of a cross section of a yarn.

The preferred carpet yarns of this invention are comtinuous textured multifilament thermoplastic yarns having the above described filament cross section, a total yarn denier between 2,000 and 4,500, individual filament denier between 7 and 25, packaged crimp index between 4% and 11%, and a relaxed crimp index between 8 and 15 percentage units greater than the packaged crimp index.

The crimped filaments of carpet yarn of the invention are characterized in having a zig-zag or saw-tooth type of crimp configuration consisting of crimp points between 'otherwise straight portions of filament. The crimp points, under polarized light, display a sharply defined strain zone. When successive cross-sections cf filament are taken and examined by X-ray diffraction techniques, it is found that the X-ray pattern changes abmptly at the crimp point, where is becornes considerably more difluse than in the straight portions, indicating a decrease in inter-crystalline orientation of at least about 20%. The frequency of -occurrence of crimp points, and the average 0f the angle B determined by the straight sides (b) at crimp points (a) are definitive of the crimp characteristics of the fibers. The average nurnber of crimp points per unit unextended length of fiber, and the average value of the angle B may be ascertained by mi-croscopic examination. As a more convenient indication of crimp characteristics ihowever, the crimp index method may be ernployed wherein a length of fiber is measured hanging under an added load =of 0.1 gram per denier for a period of 2 seoonds (length L Under which condition the crimp angle is fairly straightened to 180, and rneasuring the length of the same ber hanging under no added Weight after an elapsed time of at least 15 seconds from any crimp index:

The yarns of this invention Will ordinarily be provided for cornrnercial utilization on convolutely Wound packages such as bobbins, pirns, spools, bearns, and the like. The crimp index of the packaged yarn prior to utilization or subsequent treatment Will be referred to herein as the packaged crimp index.

Under yarn relaxing conditions, the yarns of this invention will undergo a permanent decrease in the angle B, and thus an increase in crimp index. It has been found that an increase in the crimp index of at least 8 percentage units is required to secure satisfactory resiliency and covering power in carpets, but crimp indexincreases greater than about 15% cause an undesirable matting effect. The increased value of the crimp index may be referred to as the relaxed crimp index. Relaxing conditions useful in increasing the crimp index of the yarns of this invention include conditions of zero yarn tension, elevated temperatures above the second-order glass transition temperature of the yarn, and preferably contact with plasticizing agents. Specific relaxing treatments include exposure of carpets to dry heat or steam, and immersion in bot aqueous scouring baths or dyebaths. Treatment temperatures between 125 C. and 250 C. may be employed for durations of several seconds to an hour, depending upon the nature of the yarn and other factors. Polycapnoamide yarn is especially preferred in the practice of this invention in view of its good response to the relaxing conditions encountered in carpet finishing operations such as dyeing and steaming.

Although I do not Wish to be bound by theoretical explanations, it is felt that the novel cross-sectional configuration of this invention exerts a beneficial moderating eflect on the forces at the filament crimp points which tend to contract the crimp angle upon exposure of the filaments to relaxing conditions. Thus, the filaments of this invention, having a line of symmetry in their crosssectional configuration, undergo a smaller increase in crimp index upon relaxation than centrally symmetrical filaments having circular, Y-shaped, tri-lobal, or clover leaf configurations, and undergo a greater increase in crimp index than tri-lobal filaments having an angle (u) greater than The trilobal configuration imparts rigidity toward bending, and this rigidity translates into greater resiliency in the carpet structure. The rounded nature of the lobes permits the individual filaments t0 freely pass over one another and thereby intermingle With adjacent filaments to secure greater covering power during carpet after-treatment. The absence of sharply defined internal cusps or corners within the filament comfiguration 0f this invention, such as exists in ordinary three-leaf clover and Y-shaped configurations of the prior art, minimizes the tendency 0f the yarns of this invention to attract and hold dirt. The complete absence of straight portions in the cross-sectional configuration facilitate transient compaction of the filament bundle to enable assage through the narrow eye of a tufting needle. lt is surprising that even though the filaments have no flat surfaces, they aflord a degree of luster highlight which surpasses angular, r-ound, or centrally symmetrical trilobal filaments.

The yarn product of this invention may in general be prepared by melt extruding a thermoplastic polymer of fiber forrning viscosity downward through spinnerette plates as illustrated in FIGURE 3 of the drawings, centaining orifices as illustrated in FIGURES 4 and 5 of the drawings, consisting essentially of three closely positioned separate circular holes arranged in an isosceles triang'le; and employing spinning conditions such that a cont'rolled 1 degree of coalesence of the three separate extrudate streams occur prior to solidification of the polymer.

The degree of coalescence of the three separate extrudates varies depending upon spacing of the three extrudates, spinning temperature, rate of extrusion, rate of extrudate cooling, viscosity of the extruded polymer. It will be appreciated, accordingly, that these factors must be maintained under close control to assure uniform results.

Spacing, over the critical portion of travel, is largely a matter of spacing of the holes; but also involves the socalled nodular eifect, whereby a melt extruded under high pressure through a narrow passage tends to expand or thicken upon emergence from the passage. Cylindrical or slightly downward tapering holes are preferred. Holes with diameters between about 0.005 and about 0.02 inch and length between about 0.01 inch and about 0.05 inch are employed for production of carpet yarn. The separation between peripheries of the nearest adjoining holes is between 0.001 and 0.005 inch.

Spinning temperature is suitably in the range 250"- 285 C., preferably 255 275 maintained constant by jacketing the pack containing the filter and splnnerette.

Extrusion rate is controlled by a precision feed and take-up system, and cooling rate is controlled by a nonturbulent flow of constant temperature, constant humidity gas introduced into the spinning tower, especially air.

Polymer viscosity is a highly important factor and should be controlled within 2 units of Formic Acid Relative Viscosity, preferably within 11 unit. For polycaproamide, suitable polymer viscosities, as measured in terms of Formic Acid Relative Viscosity in aqueous 90% formic acid solution of 11 grams of polymer in 100 m1. solvent at 25 C. (ASTM procedure D-789-53T) are between 30 and 75. The polycaproamide should contain not over 0.2% moisture and not over about 2% monomer.

The included angle -(a) of the filament cross section of- FIGURE 1 is determined by the corresponding angle between the centers of the three holes in the spinnerette orifice, which accordingly is between 80 and 120, especially about 90.

The extruded filaments are taken up under W tension not above about 0.1 gram per denier, to avoid undue stretching. Thereby the natural tendency under these spinning conditions of the molten filaments to thicken contributes to the desired quick, controlled coalescence. Over a first zone in the spinning tower, the freshly extruded filaments are contacted with a non-turbulent counter-current flow of air which causes their solidification at the exterior. This air acts to carry 01T monomer vapors from e.g. polycaproamides, thereby av-oiding later difficulties which would develop from excess quantities of monomer in the polymer. This first zone will generally be about 3 inches to about 1 or 2 feet long, such as to complete or substantially complete the exterior solidification. The filaments Will then pass into a non-turbulent stream of co-currently flowing gas, moving downward with at least twice the volumetric flow rate of the countercurrent stream of gas and Will be further cooled thereby over a length of travel at least five-fold the travel in the co-current gas stream.

The yarn thus prepared Will be subjected to drawing Operations, With or without application of heat, which orient the molecules of the polymer and thereby impart improved strength to the yarn.

T0 obtain the crimped yarn of my invention, the drawn yarn resulting from the above operations is subjected to a crimping operation which imparts to the filaments angular crimps, at temperatures not below 100 C. and not above the heating zone temperatures described below. Suitable crimping processes include stuffer-box methods such as described in Pike U.S. Patents 3,037,260 of Inne 5, 1962 and 3.031,734 of May l, 1962; jet-impingement methods such as described in Hallden et a1. U.S. Patent 3,005,251 of October 24, 1961; belt 01 gear crimping processes such as described by Shattuck U.S. Patent 2751661 of Inne 26, 1956; and other processes analogous thereto.

The crimped yarn thus produced is then subjected to a stresslng operation which imparts the latent contraction response properties to the yarn -by a process wherein the crimped yarn is removed from the crimping chamber and cooled in relaxed form; the yarn is then tensioned to straighten it and passed through a heating zone maintained at temperatures above the second order transition temperature of the yarn, and preferably at temperatures within about 50 C. below the polymer melting point. For polycaproamide, the melting range is about 215225 C. The residence time of the yarn in this stressing zone is generally in the range of about 3 seconds to about 30 seconds. The yarn is subsequently cooled while still under tension such as to maintain its extended form.

The stressing process is generally found to afiect an average reduction in the crimp angle, B, of between 5 and 15 The yarn may subsequently be twisted, entangled, randomized, or sized prior to packaging. Various finish compositions may be applied to the yarn eitl1er prior or after crimping to facilitate the various textlle operations.

In the absence of well recognized objective quantitative tests for the various desirable characteristics of fl00r coverings, the evaluation of the several advantages secured by the practice 015 this invention were found to be most reliably ascertained by a subjective rating system wherein 6 persons would study the same .sample for Same characteristic. Ratings were then made on a scale of from 1 to 5 With a rating of 5 representing a high degree of the desired property and a rating of l indicating an unsatisfactory level for that particular characteristic. The average value of the six persons would then constitute the rating of a particular property for a particular sample. In this fashion, ratings were made of such characteristics as luster highlights, covering power, resilieney, soiling propensity, and matting or pull down.

The following specific examples are given to illustrate preferred methods of carrying out the present invention. lt is to be understood however, that the examples are not to be considered as limitative of the scope of the invention. Percent in the examples means percent by weight in referring to concentrations.

EXAMPLE 1 Polycaproamide polymer was used havlng a moisture content of 0.05%0.10%, total constituents extractable by hot water of 1%2%, an lFormic Acid Relative Viscosity of 57. The polymer contained about 0.2% titanium dioxide dulling ageht. The polymer was melted in a screw extruder and themelt at 285 C. was'forwarded at a pressure of 1800 p.s.i.g. through a sand filter to a spinnerette plate upon which 70 three-hole orifices were arranged in 2 concentric circles, 30 in a 3 /2 inch diameter circle and 40 in a 4 /2 inch diameter circle, the 3 holes forming an isosceles triangle approximately bisected by the circle. The pack containing the filter and spinnerette was jacketed with high boiling liquid (Dowtherm) held at constant temperature of 257 C.

Bach of the 70 orifices consisted of a cylindrical inlet passage about 1 4 inch deep and %2 inch in diameter, leading to the groups of 3 holes, each of which was about 0.02 inch deep and about 0.014 inch in diameter. The 3 holes of each group formed an isosceles triangle with apex angle of and each leg 0.0165 inch long, leaving a separation of 2.3 mils (0.0023 inch) between the periphery of the center or apex hole, and that o-f each of the outerholes.

The f;ace of the spinnerette was coated with a fluid polysiloxane release agent. The throughput was 32.5 lbs./hr. of polymer. The freshly extruded filaments descended a spinning tower into which air at 82 F. and 65% relative humidity was admitted about 8 inches below the spinnerette. The tower was 9 inches in diameter and 15 feet long. A minor portion (about /s) of the entering air was drawn upwa-rd as a neu-turbulent stream in countercurrent contact with the descending filaments; and the major ortion of the entering air floweddownward as a neu-turbulent stream in cocurrent contact with the descending filarnents. The 3 filaments of each group partially coalesced and began to solidify, forming trilobal cross section, within one inch of the spinnerette face. As the resulting coalesced filarnents descended in the -tower they further solidified, maintaining trilobal cross section.

The yarn ernerging from the spinning tower contacted a ceramie roll which applied a lubricating finish, and the yarn then passed to a driven roll and was convolutely wound onto a package -at 1850 ft./min. and tension of 90110 grarns. The yarn thus obtained, having denier of 4080, was drawn over a inch diameter drawpin at delivery rate 1536 ft./min. which was 3.7 .II1S the feed rate, to secure a drawn yarn denier of 1200 Wherein each of the 70 filaments had a denier of 17. During -drawing the yarn was passed in 5 wraps over a shoe-type heater maintained at 185190 C. in accordance with Wincklhofer U.S. Patent 2,859,472 of November 11, 1958.

The trilobal cross section of the resulting yarn, on

the average, had included angle (a) of about 90; ratio of lobe radius to extension of about 0.65, and about 750 of lobe arc. All lobes had substantially equal radii cf about 8.5 microns. The yarn was then subjected to a continuous stulfer box crimping Operation employing apparatus essentially as described in Pike U.S. Patent 3,037,260 of Inne 5, 1962, and process conditions essentially as described in Pike U.S. Patent 3,031,734 of May 1, 1962. Specifically, 60 separate ends of the above prepared yarn, combined into 20 three-end groups, were continuously fed to a preheating chamber containing superheated steam at a temperature of 172 C. The yarn emerging from the preheating chamber, at a temperature of about 140 C. was directly fed as 20 three-end groups to the nip rolls of a crimper operating with a nip roll pressure of 15 p.s.i.g. and an exit gate pressure of 35 p.s.i.g. and maintaining a temperature of about 125 C. in the crimping chamber. The yarn emerging from the stuffer box crimper was then cooled in compacted form to a temperature f 70 C. The 20 three-ply yarns were then separated and continuously forwarded through a stressing chamber containing steam at 1 p.s.i.g. at temperature of 175 C., and wherein the tension on each yarn end was, 775 grams. The residence time of the yarn in the chamber was about 17 seconds. Upon emergence from the stressing chamber pull rolls, the yarn was tensioned to maintain the extended form while cooling, and the yarn was then wound convolutely onto tube supports. The packaged yarn had a denier of approximately 3600 and consisted of 210 individual filaments. The yarn had a packaged crimp index of 6.7% and a relaxed crimp index, determined after subjecting a sample of yarn to boiling water for 1 hour under no tension, of 20.7%.

The packaged yarn thus prepared was employed in making a loop pile tufted carpet having 6 tufts per inch and 20 ounces of fiber per square yard of carpet, employing a woven jute backing of 12 ounces per square yard. The tufting needle had an oval shaped eye inch high and inch wide and operated at a rate of 520 tufts per minute. Performance cf the yarn during the tufting operation was excellent, without occurrence of any stoppages of operation due to the inability of the yarn to ass freely through the eye of the needle. A sample of the tufted carpet was then scoured at 212 F., dyed blue, and a standard latex dispersion was applied to the backing of the sample. The carpet sample was then evaluated for various characteristics.

Evaluation of soiling propensity was made based upon carpet samples which were carefully exposed to normal usage within building corridors for a controlled extent Cf trafific thereup0ri, and determining the extent cf soiling of the sample in comparison with a sample of the original carpet and samples of other carpeting fabricated to the same general characteristics but made with round cross section filaments instead of the filaments of this invention.

Covering power was judged by visual determination of whether the white colored carpet backing could be seen through the pile surface when viewed from above.

The luster highlight rating was determined by inspection of the carpet sample at a 45 angle in ordinary daylight, in comparison with control samples of round cross section fiber carpeting and centrally symmetrical trilobal cross section fiber carpeting. The carpet of this example showed in uniquely high degree a luster highlight characterized by diamond-like sparkle or crystals of light, conveying an appearance of depth by reason of the contrast of sparkles against the darker surrounding background. Luster highlight results from refraction of light rather than the simple reflection, Which produces luster.

The evaluated characteristics of the carpet sample of this example, in comparison with various control samples, are presented in Table I.

Table l [Property ratings] Luster Resil- Covering Soiling Sample High iency Power Resistlight ance A. Oarpet ot' This Example.- 4. 5 4. 2 4. 1 3. 4 B. Round Filarnent Contr 1 1.2 1.6 3.2 4.3 C. Symmetrical Trilobal Control 2 3. 7 4. 6 4. 4 3. 5 D. ThreeLeaf Clever Contlol 3 3. 3 3. 7 3. 8 1.8 E. Y-shaped Control 4 3. 6 4. 0 3. 8 3. 4 F. Fused fi-filament Con- A carpet prepared as in this example employing yarn prepared in accordance w1th this example with the exception that the filaments have a, c1reular cross-section.

-Same as 1 except that the filaments have a centrally syrnmetrical trll0bal cross-Section resembling Flgure 2 01 U.S. Patent 2939,201.

Same as 1 except that the filaments have a centrally symmetrical three-lauf clever cross-seetion resembling Figure 2 of U.S. Patent 2968,857

1. Same es 1 except that the filaments have a Y cross-section resembling F1gure 1 of U.S. Patent 2,828,752.

5. Same as 1 exeept that the filaments eonsist of six circnlar filaments fused together resembling Figure 1 01 U.S. Patent 2,959,839.

As the data of Table I indicate, filaments having a cross-sectional configuration within the purview of this invention exhibit a surprisingly high luster highlight, and good ratings of resiliency, covering power, and soiling resistance in comparison with previously known crosssectional configurations.

EXAMPLE 2 In order to determine the effect of the ratio of lobe radius to extension on the characteristics of the filaments cf this invention, a series of yarns were prepared utilizing the spinnerette and spinning conditions of Example 1 but employing polycaproamide polymers of various viscosities. It was found that the ratio of lobe radius to extension would increase with a decrease in the Formic Acid Relative Viscosity of the polymer employed. It was also found that, unless the polymer contained less than 0.2% moisture, unsatisfactory coalescence of the three extrudate streams would occur. The yarns thus prepared, all having an angle (a) of were crimped, stressed and woven into carpets in accordance with the method 0f Example 1..

The nature of the samples prepared, and test results obtained therewith are presented in Table II.

takably diminished luster highlight rating. Thus, samples L, P, and R, which are outside the scope of this invention,

1 In units 01 formic acid relative viscosity.

2 Carpet sample exhibited undesirable pull-down and an unsatisfactory lolt rating 01 3 Carpet sample exhibited unsatisfactory covering power rating of 1.5. 4 All polymer samples additionallly contained 0.85% e-oaprolactam.

As the data of Table II indicate, the ratio of lobe radius t0 extension is a critical parameter in the securernent of the desired advantages of this invention. Ratios above about 1.0 result in diminished luster highlight, and an excessively high increase in crimp index upon relaxation which results in pull-down or matted carpet appearance. Ratios below about 0.60 also result in dirninished luster highlight, and in addition have inadequate response to relaxing conditions to provide satisfactory covering power.

EXAMPLE 3 are generally characterized in having luster highlight ratings below about 4. The data of Table III is also noteworthy insofar as it establishes that the desirable quality of luster highlight is dependent upon the novel configuration of the filament and that factors such as polymer type, crimp characteristics, and fabric construction are not comtrolling on this characteristic.

EXAMPLE 4 The processability of yarn in tufting operations was studied employing the tufting conditions of Example 1 011 various polycaproamide yarn sarnples. of processability, the numberof stoppages or quality defects due t0 the behavior of the yarn was counted per 10 sq. yards of tufted carpet. Satisfactory operation is generally considered to require less than 24 occurrences of stoppage or defects per 10 sq. yards. The nature of the samples tested and the results obtained therewith are presented in Table IV. All yarn samples tested had turn per inch Z twist, and contained equal quantities of a standard mineral oil-based yarn lubricating finish.

T able IV Cross seetion 1 Pack- Yarn, Filaaged Tufting Process- Sample Denier ment, Orimp Carpet Quality 2 Denier a, Ratio Are 3 Index,

degrees percent 12 90 O. 425 8. 4 Poor covering power. 12 O. 85 425 8. 4 00d. 12 90 0. 85 425 8. 4 D0. 12 90 0. 85 425 8. 4 '1uiting defeets. 30 90 0.90 410 6. 5 Poor covering power 5 90 0.80 450 10. 4 Poor resilieney.

1 Cross-seetion 0f this invention eorresponding to FIGURE 1,

defined in terms of the angle a, the ratio o ratio 01 lobe radlus 1:0 extension, and the degrees 01 lobe am.

2 After finishing by the method of Example 1. 3 'Ihe lobe am value is an approximate number due 120 the d1fii0ulty m ascertaining the exact location o1 the six infleetion poiuts.

Table III Angle Luster Sample Polymer (er) Highdegrees light Rating 138 2.8 82 4. 4 4. 2 0 82 4. 5 Polypropylene 7 3. 7 -.---do 115 4.2 do 128 1.7 Poly (ethylene terephth alate) 82 4. 0

As the data of Table III indicate, the unexpected criticality of the angle (a) is such that angles outside the As the data of Table IV indicate, samples U and V within the purview of the crimped carpet yarns of this invention produce good tufting processability and good quality carpets. Sarnple T, having a denier below the preferred range of this invention for crimped carpet yarn,

produees carpets having poor covering ower; and sample W, having a denier above the preferred range, performs unsatisfactorily in the tufting operation. Samples X and Y illustrate the eflfects of filament deniers above and below the preferred range respectively. The data in general illustrates the critical requirernents of yarn and filan1ent denier characteristics in the securement of crirnped carpet yarns which not only process well but also yield good quality carpets.

In Order to secure a satisfactory increase in crirnp range of 80120 of this invention produce an unmis- 75 index of between 8 and 15 percentage units upon ex- As a measure 1 posure of the yarn to relaxing conditions, it is essential that the yarn contain the angular crimps prescribed herein containing sharply defined internal strains as may be detected by polarized light, and crystalline disorientation at the crimp points detectable by X-ray diffraction. Although ordinary crimping processes such as the stuiferbox method Will provide angular crimps, these methods generally do not impart suitable internal strain at the crimp points. By the process of this inventiou internal strain is imparted to the angular crimps by a thermal stressing operati on involving controlled eonditions of temperature, tirne and stress. Although the theoretical factors underlying the stressing operation are not clearly understood, it is felt that the polymer in the periphery of the fiber at the crimp point becomes plasticized, enabling the flexural widening of the angle (B) by the tension applied to the yarn. Upon emergence frorn the heated stressing zone under tension, the peripheral polymer rehardens and thereby encases or freezes-in the internal strain or mechanical otential energy at the crimp point. Upon subsequent exposure cf the stressed yarn thus prepared to relaxing temperatures, the peripheral polymer layer Will again become plasticized and, under the zero tension of relaxation enables the internally strained ortion to return to an unstrained condition. The eifect is thereby analogous to a stretched spring which, upon removal of restraining forces, returus to its original length.

Although the cornbination of the novel cross-sectional configuration of this invention with angular strained crimps in a thermoplastic fiber aifords unexpected syner gistic improvements in the production of floor coverings,

filaments having the cross-sectional configuration of this invention are useful in numerous other textile applications in staple and continuous filament homofiber and blends in uncrimped or crimped form. In view of the desirable aesthetic qualities of luster highlight imparted by the ber, typical textile applications would include apparel products Such as woven suitings, shirtings, sheeting and lingerie, tricot, circular knitted fabrics, broadcloths, satins, and the like. In view of their relatively high surface area, stiifness, and strength, the filaments of this invention are useful in industrial textile applieations such as sewing thread, fiber-reinforced laminates, tire eord, upholstery, drapery, curtains, ducks, and other applications.

The yarns may be made to contain various additive ingredients which irnpart specialized properties. For example, ingredients which may be added to the yarn either by incorporatiug within the polymer prior to spinning, or by after-treatments of the yarn or fabric include flarne retardent agents such as compounds of antimony, phosphorous, and halogens; titanium dioxide delusterant; antistatic agents; adhesion promoting agents such as isocyanates and epoxides; heat and light stabilizers such as inorganic reducing ions, metal ions such as manganese, copper and tin, phosphites, and organic amines such as alkylated aromatic amines and ketone-arornatic amine condensates; therrnally stable p1gments such as Quindo Magenta (Allied Chemical Corp.) and inorganic pigments; fluorescent agents and brighteners suchas Tinopal PCR; cross-linking agents; bacteriostats such as phenols and quaternary amines; colloidal reinforcing particles; antis-oiling coatings such as colloidal silica and boehmite; and otl1er known additives and treatments. lt is essential however, that essentially no volatile ingredients such as water or solvents be contained by the polymer prior to extrusion since these are deleterious to satisfactory extrudate coalescence. The presence of plasticizers 110W- ever are beneficial to extrudate coalescence, and can be removed if desired after filament formati=on. In the case of polycaproamide polymer, the presence of about CJI 0.5 %2% of monomeric lactam which acts as a plasticizer, facilitates extrudate coalescence, and this represents a highly preferred aspect of the present invention.

Thermally stable flow controlling agents or surfaceactive agents which decrease surface free energy may be included within the polymer prior to extrusion to increase the extent of extrudate coalescence, and thereby increase the ratio of lobe radius to extension. Exarnples of such agents include: metal salts of long chain aliphatic carboxylic acids, long chain aliphatic alcohols, long chain aliphatic amides, and fluorinated and other surface active agents.

The yarns of this invention can be admixed with yarns of round cross section er of various modified cross sections, of the same or different denier and of the same or difi?erent chemical composition to produce various special effects.

As many widely different embodiments may be employed er made without departing from the spirit and scope of this invention, it is to be understood that the invention is to be in no wise restricted save as Set forth in the appended clairns.

I clairn:

1. A multifilament yarn of polycaproamide having a Formic Acid Relative Viscosity between about 30 and 75, the filaments of said yarn having trilobal cross section consisting of a center lobe and two pendant lobes, each lobe bounded by a circular arc which defines a center of curvature and radius of curvature of each lobe, said centers of curvature being positi-oned to define an included angle at the center of said center lobe between and said lobes being separated by peripheral arcs of inverse curvature which arcs between center lobe and pendant lobes are essentially identical and have larger radii of inverse curvature than does the arc between the two pendant lobes; said cross section having a line of symmetry and no center of symmetry, said line of symmetry passing through the center of curvature of the center lobe and bisecting the region of inverse curvature between the pendant lobes, the ratio of the radius of curvature of the pendant lobes to the distance of separation between the centers of the center lobe and pendant lobe being between 0.60 and 1.0, said cross section having between 400 and 750 of circular lobe arc; said yarn having individual filament deniers between 7 and 25 said filaments having angular crirnps such that the packaged crimp index is between 4% and 11%, and having a relaxed crimp index between 8 and 15 percentage units greater than said package crimp index; said angular crimps possessing at the crimp points sharply defined intern-a1 strain as may be detected by polarized light, and sharply defined zone of crystalline disorientation at said crimp points; said yarn having denier between 2000 and 4500.

2. A loop pile tufted carpet wherein the pile is the yarn of claim 1.

References Cited by the Examiuer UNITED STATES PATENTS 2939201 6/60 Holland 161177 XR 2968857 1/61 Swerdlofr et al. 161-173 XR 3,023075 2/62 Larman et al. 18-53 3038239 6/62 Moulds 161177 3039524 6/6-2 Belch et al. 161-177 3084,993 4/63 Dawson et al. 1854 FOREIGN PATENTS 731,930 6/55 Great Britain. 816,877 7/59 Great Britain.

ALEXANDER WYMAN, Primary Examiner. EARL M. BERGERT, Examiner. 

1. A MULTIFILAMENT YARN OF POLYCAPROAMIDE HAVING A FORMIC ACID RELATIVE VISCOSITY BETWEEN ABOUT 30 AND 75, A FILAMENTS OF SAID YARN HAVING TRILOBAL CROSS SECTION CONSISTING OF A CENTER LOBE AND TWO PENDANT LOBES, EACH LOBE BOUNDED BY A CIRCULAR ARC WHICH DEFINES A CENTER OF CURVATURE AND RADIUS OF CURVATURE OF EACH LOBE, SAID CENTERS OF CURVATURE BEING POSITIONED TO DEFINE AN INCLUDED ANGLE AT THE CENTER OF SAID CENTER LOBE BETWEEN 80* AND 120*; SAID LOBES BEING SEPARATED BY PERIPHERAL ARCS OF INVERSE CURVATURE WHICH ARCS BETWEEN CENTER LOBE AND PENDANT LOBES ARE ESSENTIALLY IDENTICAL AND HAVE LARGER RADII OF INVERSE CURVATURE THAN DOES THE ARC BETWEEN THE TWO PENDANT LOBES; SAID CROSS SECTION HAVING A LINE OF SYMMETRY AND NO CENTER OF SYMMETRY, SAID LINE OF SYMMETRY PASSING THROUGH THE CENTER OF CURVATURE OF THE CENTER LOBE AND BISECTING THE REGION OF INVERSE CURVATURE BETWEEN THE PENDANT LOBES, THE RATIO OF THE RADIUS OF CURVATURE OF THE PENDANT LOBES OF THE RADIUS SEPARATION BETWEEN THE CENTERS OF THE CENTER LOBE AND PENDANT LOBE BEING BETWEEN 0.60 AND 1.0 SAID CROSS SECTION HAING BETWEEN 400* AND 750* OF CIRCULAR LOBE ARC; SAID YARN HAVING INDIVIDUAL FILAMENT DENIERS BETWEEN 7 AND 25, SAID FILAMENTS HAVING ANGULAR CRIMPS SUCH THAT THE PACKAGED CRIMP INDEX IS BETWEEN 4% AND 11%, AND HAVING A RELEXED CRIMP INDEX BETWEEN 8 AND 15 PERCENTAGE UNITS GREATER THAN SAID PACKAGE CRIMP INDEX; SAID ANGULAR CRIMPS POSSESSING AT THE CRIMP POINTS SHARPLY DEFINED INTERNAL STRAIN AS MAY BE DETECTED BY POLARIZED LIGHT, AND SHARPLY DEFINED ZONE OF CRYSTALLINE DISORIENTATION AT SAID CRIMP POINTS; SAID YARN HAVING DENIER BETWEEN 2000 AND
 4500. 